1. Field of the Invention
The invention relates in general to oil well drilling equipment, and in particular to pipe handling machines for handling sections of drill pipe, drill collars, and the like.
2. Description of the Prior Art
During the drilling of oil wells, it is necessary to periodically move sections of drill pipe from a setback area to the well center, so that the sections of pipe can be added to the drill string. Also, whenever the drill string is removed from the well, the sections of pipe must be returned from the well center to the setback area for temporary storage.
Generally, sections of drill pipe are moved between well center and the setback area in an essentially vertical position. The sections are lifted by a pipe elevator attached to the upper end of the section. The elevator is suspended from a travelling block in a derrick. When the upper end of the pipe section is being lifted, the lower end of the pipe tends to sway, creating a hazard to personnel and to equipment. Therefore, the lower end of the section must be controlled in some manner.
Manual control of the lower end of the section is dangerous and unreliable. The large mass and unpredictable movements of the pipe section make it difficult for rig hands to control a section. This problem is particularly acute on offshore rigs, which are subject to severe pitching and rolling due to high winds and waves.
A number of racking arms and similar machines have been developed to mechanically handle vertically suspended pipe sections. For example, U.S. Pat. No. 3,840,128 shows a racking arm for handling drill pipe. This device is supported on a pedestal, permanently mounted on the rig floor. The racking arm thus cannot be easily moved out of the way. On a crowded rig floor that may be a serious problem.